1. Field of the Invention
The present invention relates to a moving picture experts group (MPEG) decoder, and more particularly, to an MPEG decoder for caption display and a decoding method of the same.
2. Description of the Related Art
A video stream, which is decoded by an MPEG video decoder, has a structure in which a sequence header representing the start of a video sequence and a plurality of groups of pictures (GOPs) are consecutively arranged. Each GOP includes a GOP header and a plurality of pictures such as an I picture, a P picture, and a B picture.
The GOP header includes a user data area. For example, a twenty-first horizontal line in a video stream can be used as the user data area. This user data area is usually used to store caption information.
Generally, a caption function denotes a function of displaying, for example, a Korean or English-language caption on a display screen. In conventional systems, in order to perform a caption function, user data is extracted from the header information of the video stream. The extracted user data is applied as caption data to a video encoder, and generated as an internal caption signal.
FIG. 1 is a schematic block diagram of a conventional MPEG decoder. Referring to FIG. 1, the conventional MPEG decoder includes an MPEG A/V demultiplexer 100, an audio digital-to-analog converter (DAC) 110, a video decoder 120, a header first in first out (FIFO) memory 130, a central processing unit (CPU) 140, and a video mixer 150. Also, the video encoder 160 is shown in FIG. 1 for convenience of explanation.
The MPEG A/V demultiplexer 100 demultiplexes an M-PEG stream applied from an input terminal MIN into a digital audio stream and a video stream. The audio decoder 105 decodes the audio stream applied from the MPEG A/V demultiplexer 100. The audio DAC 110 converts the decoded digital audio stream applied from the MPEG A/V demultiplexer 100 into an analog signal and outputs the analog signal via an audio output terminal A—OUT.
The video decoder 120 decodes the video stream applied from the MPEG A/V demultiplexer 100 and extracts user data USER—DATA from the GOP header of the video stream. The header FIFO memory 130 stores the user data USER—DATA extracted from the GOP header. The CPU 140 receives the user data USER—DATA from the header FIFO memory 130 and outputs the user data USER—DATA as caption information if the user data is determined to be caption information. The video mixer 150 mixes a video signal decoded by the video decoder 120 with on-screen-display (OSD) data applied from an OSD controller (not shown) and outputs the result to the video encoder 160. The video encoder 160 encodes the output of the video mixer 150 and the user data USER—DATA, that is, caption data, output from the CPU 140, and outputs the result of encoding via a video output terminal V—OUT.
In the conventional MPEG decoder shown in FIG. 1, user data USER—DATA extracted from the header of an MPEG video stream is directly output to the video encoder 160 in order to perform a caption function. The caption function is therefore achieved by expensive encoders or televisions which are specially manufactured to include the caption function. Thus, in the prior art, ordinary televisions cannot perform a caption function.